The growth of the distributed power market has lead to increased research in the area of power modules. As a result, the power density of power modules has increased four times in the past few years, and the efficiency of power modules has significantly increased due to the improvement of current semiconductor devices and the utilization of synchronous rectification for power module applications. As logic integrated circuits have migrated to lower working voltages in the surge for higher operating frequencies and as overall system sizes have continued to decrease, power supply designs with smaller and higher efficiency power modules have increased in demand.
In an effort to improve the efficiencies and increase power densities, synchronous rectification has become necessary for these types of applications. Synchronous rectification has gained great popularity in the last ten years as low voltage semiconductor devices have advanced to make this a viable technology. The power electronics design engineer, however, is still challenged to design power modules with high power density, high efficiency, low output voltage and high output current.
Power modules having synchronous rectification have generally comprised a single winding output inductor connected to the output load of the synchronous rectifier circuit. This has generally been the most popular approach because of its simplicity and reduced part count. A power module configuration known as a "quarter brick" can be used in applications where board space is limited. One version of a quarter brick power module measures 2.28" long by 1.45" wide by 0.5" in height.
The quarter brick power module, as well as other similar power module configurations, typically places the input pins and output pins on opposite ends of the assembly. Essentially, the packaging and layout constraints require the output inductor to be terminated at opposite ends with respect to both the input and output sides of the inductor. This configuration results in a winding configuration with an extra half turn which, in turn, effects the resultant magnetic flux patterns of the inductor core. In particular, the inductance of the fractional turn created by the termination of the output inductor increases with current so that the inductor is easily saturated.